Step 18:

Step 19:

We are finally done! Plug the +12VDC power supply into the Arduino's power jack and admire your work! Make sure that the USB cable is NOT plugged in t...

Step 17:

Finally we will connect the Arduino to the first register (the very far-right one, or the bottom one in the schematic/diagram). Connect digital pin 8 of the Arduino to pin 12 of the shift register. Then connect pin 11 of the Arduino to pin 14 of the shift register. Lastly, connect pin 13 of the Arduino to pin 11 of the shift register. See images if you get lost.

Sorry, I can't match up the diagram and the text. According to the text, both register pins 12 and 14 are connected to Arduino pin 8. According to the picture, register pin 12 is connected to Arduino pin 8 register pin 14 is connected to Arduino pin 11.